Coke and Pepsi brands declined 2% and 4.5%, respectively, by volume in the US in 2017, according to Beverage Digest's annual report, which was released on Monday. Meanwhile, Aquafina increased 2.6% by volume and Poland Springs grew 2.5%.

Overall, the carbonated-soft-drink category declined 1.3% by volume, while bottled water grew 6.2%.

The rise of bottled water has been a long time coming. After a decades-long growth streak, bottled water sales by volume finally surpassed sales of soft drinks in 2016, reaching 12.8 billion gallons, according to research and consulting firm Beverage Marketing Corporation.

Companies selling bottled water, he argued, have managed to convince people that buying water is a healthier choice than sugary soda.

But, Jewell wrote, the comparison is a case of false equivalence. Bottled water isn't simply an alternative to soda — it's an alternative to tap water, which is free and much more eco-friendly. By buying bottled water, consumers aim to establish themselves as savvy and health-conscious, even though they could simply drink a glass of tap water that is 2,000 times less expensive.

Despite this, brands like Pepsi-owned Aquafina and Nestlé-owned Poland Springs are thriving thanks to health-centric marketing and the convenience they offer. As Americans increasingly ditch sugary sodas due to health concerns, bottled water provides a different option — and a new way for beverage companies to boost profits.

Beverage giants like PepsiCo and Coca-Cola are forced to balance nurturing the growth of smaller bottled water brands and stemming the decline of soda brands. Americans still bought almost four times as much Coke by volume than Nestle Pure Life, the largest bottled water brand in the US by volume, in 2017.